1. Field of the Invention
This invention relates to a polishing method for removing intrinsic projections on the surface of a member such as a color filter for a liquid crystal display of STN type, TFT type or the like.
2. Description of the Prior Art
A color filter for a liquid crystal display which recently has come into wide use for various displays is generally manufactured by pigment dispersion method, dyeing method, printing method or the like. If defects such as projections exist on the surface of the color filter, the function of a transparent electrode of ITO (indium oxide-tin oxide composite) or the like is damaged when it is mounted on the color filter, which results in unsatisfactory functioning of the color filter. However even if the color filter is produced at a dust level of class 10 to 10000 (Federal specification), the projections on the color filter cannot be completely removed. Such defects on the color filter causes a color shading, a color shift, a dislocation of the filter and/or a pattern abnormality, and the the liquid crystal display cannot function even if a transparent electrode is mounted thereon. Thus the defects on the color filter lowers the yield and has been a great problem in production of the liquid crystal display.
More particularly, the liquid crystal display is manufactured by laminating a color filter a transparent electrode, picture element electrodes, a transistor layer and the like between a pair of glass electrodes with a liquid crystal layer disposed at the center. When the color filter has projections, the projections can break the transparent electrode upon lamination, which can result in a color defect.
Since these projections are "intrinsic projections" which are formed during formation of a filter film on a glass substrate by coating, printing or the like due to coagulation of dispersions or printing ink and are not simple deposits, it is difficult to wipe off the projections.
Various polishing methods have been used to smooth an uneven surface of a member depending on the material of the member, the application thereof, the performance requirement thereof and the like. However generally, an abrasive member is pressed against the surface of the member to be smoothed and slid along the surface. As the abrasive member, an abrasive tape comprising an abrasive layer formed on a flexible base is in wide use since it can slide even along a surface having an irregular contour keeping a close contact therewith.
However in the case of a color filter for a liquid crystal display, when the color filter is polished by simply sliding the abrasive tape along its surface, not only the intrinsic projections cannot be sufficiently removed but also the surface of the color filter is scratched and cuttings can scratch the surface of the color filter or can adhere to the surface of the same to cause other problems.
For example, though there are disclosed various polishing machines using various abrasive tapes in Japanese Unexamined Patent Publication Nos. 3(1991)-131463, 4(1992)-315566, 5(1993)-77153, 60(1985)-44264 and the like, polishing by these machines can result in contamination of the surface of the color filter due to the composition of the abrasive tape and/or in scratches on the surface of the color filter due to cuttings going between the abrasive tape and the color filter.